Solution metal cutting and grinding fluids



United States Fatent 3,946,225 Patented July 24, 1962 tire 3,046,225SOLUTION METAL CUTTING AND GRINDING FLUES John L. Murray, Westfield, andRoy A. Westlund, Jr.,

Roselle, N.J., assignors to Esso Research and Engineering Company, acorporation of Delaware No Drawing. Filed Oct. 8, 1958, Ser. No. 765,957

4 Claims. (Cl. 252-336) This invention relates to new and improvedsolutiontype cutting and grinding fluids. These fluids are also known inthe trade as chemical coolants. More particularly, it relates torust-inhibiting solution-type metal working fluids comprising thesynergistic combination of alkali metal nitrites and alkali salts ofN-acyl sarcosines in an aqueous solution with surface-active agents toform metal working fluids. These compositions are prepared asconcentrates which are diluted with water when used, usually with 50 to100 or more volumes of water per volume of concentrate.

The use of alkali metal nitrites and amides in preparing eflectivecorrosion-inhibiting compositions is well known in the art. It has nowbeen found that alkali metal nitrites and alkali metal salts of N-acylsarcosines in a water solution, both with and without surface-activeagents, combine synergistically to give excellent inhibition to rustingat unexpectedly low concentrations.

In the prior art, whenever alkali metal nitrites were used in metalworking fluids, a toxicity problem was encountered, with the degree oftoxicity being directly proportional to the concentration of nitriteemployed. The fluids of this invention, by having a very low nitriteconcentration, 1% and less in the diluted form, are substantially freeof this problem. Another advantage of the metal working fluids of thisinvention, resulting from the low nitrite concentration, is the abilityto use unbuifered nitrites. However, bufiers or other materials tomaintain a basic pH can be used where desired, and still remain withinthe spirit of this invention. Also, in the metal working fluids of theprior art which contain alkali metal nitrites, only those surfactantswhich could resist the oxidation attack of sodium nitrite could beemployed. This problem is not present in the metal working fluids of theinstant invention due to the very low nitrite concentration, and a widevariety of surfactants can be used.

Solution metal working fluids are contrasted to conventional soluble oremulsified cutting oils in that single phase, clear transparentsolutions are formed on dilution with water in normal use, whereassoluble oils form a milky or at best a translucent emulsion, dependingon the amount and type of emulsifier.

Solution metal working fluids offer advantages over soluble oils inseveral respects. First, soluble oils have an inherent tendency tobecome rancid as a result of bacterial attack on the emulsifiers or themineral oil itself. Solution coolants, on the other hand, can beformulated to have greater resistance to this bacterial attack andsubsequent odor formation. Second, the solutions of this invention arefar clearer than even the most translucent soluble oils, thus permittingbetter visibility of the work being machined. Transparent solutions areoften essential in grinding operations. Third, there is some indicationthat at very high cutting speeds (greater than about 400 surface feetper minute), solution metal working fluids give better tool life inlathe turning with carbide tools than soluble oils. This is believed tobe because cooling the cutting tool is more important than lubricationat these high speeds, and solutions give better cooling than do solubleoil emulsions.

The solution coolants of this invention offer a definite advantage inbehavior toward cast iron over soluble oils containing petroleummahogany sulfonate emulsifiers. Mahogany sulfonates tend to stain castiron. Also, inhibition of rust on cast iron by mahogany sulfonatesoluble oils is very difflcult. Cast iron rusts far more easily thansteel and requires particularly effective rust inhibitors. Rusting andstaining of cast iron is important because most machine tools have partsmade from cast iron which normally come in contact with the cuttingfluid. Cast iron is commonly machined without a coolant, but in someoperations a coolant is used. This places a severe quality requirementon a fluid to be used in all applications, including machining andgrinding of cast iron. The composition of this invention is particularlyeflective in inhibiting rusting on cast iron.

The solution-type metal working fluids of this invention will containalkali metal nitrites and alkali salts of N-acyl amino carboxylic acids,particularly sarcosine, in ratios in the range of 1:1 to 11:1, nitriteto carboxylate. These two specific types of alkali metal salts, whenpresent in the above ratios, will combine synergistically to preventrust at concentrations as low as 0.2% and 0.02% nitrite and sarcosinate,respectively, in the diluted fluid. Concentrations, however, as high as10.0 wt. percent nitrite and 1.0 wt. percent sarcosinate can be used inpreparing stock solutions which are subsequently diluted with water foruse as metal working fluids. A particularly eflective compositionconsists essentially of about 96.88 to 99.38% water, 0.22 to 1.25 wt.percent of a mixture of sodium nitrite and sodium lauroyl sarcosinate inratios between 9:1 and 11:1 in water solution, with 0.4 to 1.87 wt.percent of a surfactant of the polyoxyalkylene class, having a molecularweight between 3000 and 4000.

Lower concentrations in the range of 0.2 to 0.5 wt. percent nitrite and0.02 to 0.05 wt. percent sarcosinate are preferred in the working fluid.The surface-active agent may be present in concentrations ranging from0.1 to 20 wt. percent in stock solutions, but concentrations in therange of 0.2 to 0.5 wt. percent are preferred in the final metal Workingfluid. All of the above concentrations for final metal working fluid areexpressed as weight percent of the total weight of the diluted solutionof cutting fluid concentrate and water. The presence of a surface-activeagent is not essential to the formation of the rust inhibiting metalworking fluids of this invention. However, use of such agents ispreferred when the fluid is used for metal working. Solution-cuttingfluids of this invention can also contain dyes, perfumes, bactericides,sequesterants, defoamers or other materials.

The alkali metal nitrites useful in the present invention includesodium, potassium and lithium nitrite, with sodium nitrite beingparticularly preferred.

The alkali metal salt of the N-acyl amino carboxylic acid is preferablysodium lauroyl sarcosinate, however, any alkali metal salt of an N-acylamino carboxylic acid wherein the acyl group is derived from a C to Cfatty acid may be used. The alkali metal salt of an N-acyl sarcosine canbe prepared according to the following equation:

HN (CH CH CO ONa-l-RCOCI RCON(CH CH COOH+NaCl N-acyl sarcosine+NaOH-Water+ sodium N-acyl sarcosinate The alkali metal N-acyl aminocarboxylic acid salts useful in the present invention have the followinggeneral formula:

wherein R represents the alkyl group of a C to C fatty acid, Mrepresents the alkali metal, e.g., lithium, sodium or potassium, and nis an integer from 1 to 4. Examples of suitable fatty acids are capric,2-ethyl-hexoic, lauric, caprylic, oleic and stearic acids.

The surface-active agents that can be employed in the solution metalworking fluids of this invention are anionic or nonionic materials thatare compatible with the other components of the system. Suitable andreadily available surfactants may =be selected from the following list:Span products (partial esters of common fatty acids and hexitolanhydrides derived from sorbitol) and Tween products (polyoxyethylenederivatives of the Span products), both manufactured by Atlas PowderCompany; polyalkaylene glycol type fluids sold by the name of UconFluids by Carbide and Carbon Chemicals Company; alkyl phenylpolyethylene glycol ethers (typical products commercially available areCarbide and Carbons Tergitol nonionics); Ethomids (polyoxyethylenesubstituted fatty acid amides) and Ethofats (monofatty or resin acidesters of polyethylene glycols), both sold by Armour Chemical Divisionof Armour and Company, and block polymers of ethylene oxide andpropylene oxide (Pluronic materials sold by Wyandotte ChemicalsCorporation).

Surface-active agents such as alkyl ethers of polyoxyalkylene glycols,etc., are preferred. A particularly pre-' .ferred type of these ethermaterials are the copolymers of ethylene and propylene glycols which arecommercially available under the trade name of Pluronic. These materialshave the following formula:

where a and c represent integers of 2 to 300 and b is an integer ofabout 10 to 45. The molecular weight may vary considerably but generallyis between 1,000 and 30,000, with the percentage of ethylene oxidegroups in the total molecule ranging from 10% to 90%.

'The solution-type fluids of this invention can be prepared as highlyconceutrated' base solutions for further dilution in normal use. Infact, this is one of the important advantages of the fluids of thisinvention, i.e., since superior rust-inhibiting properties are shown toexist at extremely low concentrations of inhibitor, very highlyconcentrated base solutions, relative to the concentrations required foroperable metal working fluids, can be easily prepared.

The following example will help to illustrate the basis of thisinvention.

EXAMPLE I The concentrated base solution-type metal working fluid ofthis invention was prepared by combining the following materials, withstirring at room temperature:

1 A liquidpolyoxyalkylene glycol made from propylene oxide and alkyleneoxide having 40% polyoxyethylene in its molecular structure and havingabout 4,000 average molecular weight.

The concentrated base solution prepared above was diluted with tapwater, as shown in column 2 of the following table. These dilutesolutions were then subjected to testing for rust on cast iron. Saidrust test consisted of placing one drop of solution of the indicatedcompositions upon a cast iron plate which had been polished with 120then 180 grit emery cloth, followed by a washing with precipitationnaphtha. Normally, duplicate tests are run. The above plate containingthe drop of solution was then placed in a 52% relative humidityatmosphere for 1 8 to 24 hours and then removed for inspection, followedby washing with naphtha. to permit observation of stain under the rustor residue. In this test, solutions with fair to poor inhibitingproperties 5 start to rust in 15 to 30 minutes or less.

The table below shows the results obtained with dilute solutions of thecutting fluids of this invention as well as V a comparison of itsrust-inhibiting properties with other known inhibitors.

Table I Actual Concentration Tested,

Dilution of Wt. percent in Solution Concentrate, Cast Iron Test PartsWater Rust Test N 07 Per Part Sodium Rating 1 Concentrate 11-64 SodiumButler Lauroyl Pluronic Nitrite Borax sarcosinate 1 Infinite (tap 4water alone). 2.. 0 (concentrate 10 4 alone).

0 2 0 2 2 8 0 3 l0. 1. 0 0 81 t 12 13. 0.5 0 14. 0.05 0 l5. 0.02 0-1 16.0.05 0 l7. 0. 02 l2 l Rust; test rating scale: 0, no rust; l, tracerust; 2, light rust; 3, medium rust; 4, heavy rust.

The following conclusions can be drawn, from the data given in the abovetable, about the rust-inhibiting properties of the composition of thisinvention in an aqueous solution with a polyoxyalkylene surface-activeagent. This material is typical of a number of surface-active agentsthat might be used.

1) A surfactant alone has little or no effect on rust inhibition (Tests1 and 2).

(2) More than 1.0% of unbuifered sodium nitrite, used alone or with asurfactant, is necessary to inhibit rust (Tests 3, 4 and 7).

(3.) Buffered sodium nitrite is good at 1.0% concentration or higher,but poor at 0.25 to 0.50% (Tests 5, 6, 8 and 9).

(4) Sodium lauroyl sarcosinate prevents rust at 1.0%

but is only fair at 0.5% and poor at 0.1% (Tests 10, ll and 12).

(5) Sodium nitrite and sodium lauroyl sarcosinate in ratios of 1.5 :1and 10:1 combine synergistically to prevent rust at concentrations aslow as 0.2% and 0.02% nitrite and sarcosinate, respectively (Tests 13through 17).

In Tests 14 and 16, no rusting was observed where the ratio of nitriteto sarcosinate was 10:1 and the total concentration was only 0.55% byweight. When 0.55 wt. percent of either of the two components were usedalone, they were not as effective in inhibiting rust.

The nitrite-sarcosinate combination oifers the following advantages overthe obvious alternative of higher concentrations of buffered nitrite:

(1) Sodium nitrite presents a toxicity problem at higher concentration.Low concentrations of about 1% and less have been used with no harmfulresults.

(2) Solubility of many surfactants potentially useful in solution metalworking fluids is often limited by the presence of other materials inthe system, particularly ionic salts such as sodium nitrite. Thisinvention permits "5 low concentrations of nitrite and doesnot require abuffer as is usually necessary when sodium nitrite is used, although abuiier may be used which does not reduce the efiectiveness of thenitrite-sarcosinate combination.

(3) A base solution can be prepared for dilution with very large amountsof water and still maintain excellent rust inhibition, because of thesuperior rust-inhibiting properties of lower concentrations ofinhibitor.

(4) Surfactants with desirable properties but with poor resistance tothe oxidation attack of sodium nitrite can now be used because highnitrite concentrations are not necessary to provide good rustinhibition. The oxidation of surfactants by sodium nitrite is a problemwhich has seriously limited the use of many materials as surfactants.

What is claimed is:

1. An aqueous metal working fluid comprising a major proportion ofwater, 0.5 to 10.0 wt. percent of sodium nitrite and 0.05 to 1.0 wt.percent of sodium lauroyl sarcosine in ratios of 1:1 to 11:1,respectively.

2. An aqueous metal working fluid comprising a major proportion ofwater, 0.2 to 10.0 Wt. percent of sodium nitrite and 0.02 to 1.0 wt.percent sodium lauroyl sarcosine in ratios of 1:1 to 11:1 respectively,wherein said metal working fluid also has dissolved therein 0.2 to 20.0Wt. percent of a surface-active agent selected from the group consistingof nonionic surface-active agents and anionic surface-active agents.

3. A metal working fluid according to claim 2 wherein saidsruface-active agent is a polyoxyalkylene glycol having the followingformula:

where a and 0 represent integers of 2 to 300, b is an integer of 10 toand the molecular weight of said p0lyoxyalkylene glycol is between 1,000and 30,000.

4. An aqueous solution-type metal working fluid consisting essentiallyof about 96.88 to 99.38 wt. percent water, 0.22 to 1.25 wt. percent of amixture of sodium nitrite and sodium lauroyl sarcosinate in ratios ofabout 9:1 to 11:1 nitrite to sarcosinate, and 0.4 to 1.87 wt. percent ofa liquid polyoxyalkylene glycol which contains about propylene oxidegroups and 40% ethylene oxide groups and has an average molecular Weightof about 4000.

References Cited in the file of this patent UNITED STATES PATENTS2,692,859 Talley et al. Oct. 26, 1954 2,790,779 Spivak et al Apr. 30,1957 2,825,693 Beaubien et al. Mar. 4, 1958 2,931,700 Oakes Apr. 5, 1960FOREIGN PATENTS 716,354 Great Britain Oct. 6, 1954 721,526 Great BritainJan. 5, 1955

1. AN AQUEOUS METAL WORKING FLUID COMPRISING A MAJOR PROPORTION OFWATER, 0.5 TO 10.0 WT. PERCENT OF SODIUM NITRITE AND 0.05 TO 1.0WT.PERCENT OF SODIUM LAUROYL SARCOSINE IN RATIOS OF 1:1 TO 11:1,RESPECTIVELY.